Swift makes 2 sizes of rudder. A small one (50x80mm) for straight courses, and a larger one (80x100mm) for river rowing. The shaft diameter is 7.5mm, and the length of the shaft is shown for each rudder (the Prod.#). Shaft lengths may be different for wing rigger boats (W), and traditional rigger boats (T). If you try to use a Swift rudder on other boats, and the shaft is too long, use washers, or a piece of pipe to make up the length. Rudders include washers and nuts.